As an ion injecting process in the production of semiconductor devices such as an electric field effect transistor, there may be adopted a process in which an impurity ion for imparting a conductivity type, i.e., an n-type or p-type, is introduced into a semiconductor substrate using a photoresist pattern as a mask. In many cases, the semiconductor substrate has a level difference surface or an uneven surface by forming a gate electrode or a gate wiring on the substrate using a semiconductor material or a metal material such as polycrystal silicon, aluminum, and titanium nitride. When a photoresist pattern is formed on the substrate surface having a level difference (projections and recesses), a photoresist film is formed partially in a large thickness and is difficult to be formed in a homogeneous thickness. Therefore, even after exposure, development, and rinse of the photoresist film, a portion formed in a large thickness is not completely removed and tends to remain. As a result, a bottom shape of a resist pattern often becomes a footing shape and generation of a residue becomes a problem.
Conventionally known is a method for making a surface of a silicon wafer as a representative example of the semiconductor substrate hydrophobic (water repellent) by treating the surface with hexamethyldisilazane (HMDS). The silicon wafer surface exhibits hydrophilicity when a natural oxide film is formed on the surface. The above method for making the surface of the silicon wafer hydrophobic is performed because a photoresist film formed by applying a photoresist solution onto the hydrophilic surface and prebaking the resultant coating has poor adhesion with the silicon wafer.
Hydrophilicity and hydrophobicity of a substrate surface can be evaluated on the basis of a contact angle of the surface with water. Patent Document 1 discloses a photodegradable coupling agent for generating a structure with a contact angle largely changed between before and after light irradiation. The structure is liquid repellent before light irradiation and becomes hydrophilic when irradiated with light due to dissociation of a liquid repellent group. Patent Document 2 discloses a compound for forming an organic thin film capable of selectively changing the surface physical properties by being irradiated with light in order to cause a pattern forming process to be simple and to have high reliability.